Illumination unit and display

ABSTRACT

There are provided an illumination unit and a display which are capable of further uniformizing chromaticity of illumination light in a plane while suppressing a reduction in light extraction efficiency. A light modulation device bonded to a light guide plate includes a light modulation layer exhibiting a scattering property or transparency with respect to light propagating through the light guide plate. The light modulation layer is sandwiched between a pair of transparent substrates. While alignment films controlling alignment of the light modulation layer are disposed on surfaces of the transparent substrates, an electrode generating an electric field which changes the alignment of the light modulation layer is disposed on only the surface of the transparent substrate.

CROSS REFERENCES TO RELATED APPLICATIONS

The present application is a national stage of International ApplicationNo. PCT/JP2011/073486 filed on Oct. 13, 2011 and claims priority toJapanese Patent Application No. 2010-235926 filed on Oct. 20, 2010, thedisclosure of which is incorporated herein by reference.

BACKGROUND

The present invention relates to an illumination unit and a displaywhich each include a light modulation device exhibiting a scatteringproperty or transparency with respect to light.

In recent years, improvements in image quality and energy conservationof liquid crystal displays have been accelerated, and systems achievingan improvement in dark-room contrast by modulating light intensity in apartial region of a backlight have been proposed. As a main technique ofachieving an improvement in dark-room contrast, some of light-emittingdiodes (LEDs) used as light sources of a backlight are driven tomodulate backlight light based on a display image. Moreover, inlarge-screen liquid crystal displays, as in the case of small-screenliquid crystal displays, a reduction in profile has been stronglydesired; therefore, attention has been given not to a system in whichcold cathode fluorescent lamps (CCFLs) or LEDs are disposed directlybelow a liquid crystal panel, but to an edge light system in which alight source is disposed on an edge of a light guide plate. However, inthe edge light system, it is difficult to perform a partial drive tomodulate light intensity in a partial region of the light source.

CITATION LIST Patent Literature

-   [PTL 1] Japanese Unexamined Patent Application Publication No.    H6-347790

SUMMARY

As a technique of extracting light propagating through a light guideplate, for example, PTL 1 proposes a display using a polymer dispersedliquid crystal (PDLC) allowed to switch between a transmission state anda scattering state. This technique is proposed to reduce glare or thelike, and is a technique of switching between the transmission state andthe scattering state by applying a voltage to a partial region of thePDLC. However, in a backlight in PTL 1, there is an issue that lightabsorption by an electrode is considerably large, and light extractionefficiency is not increased much. Moreover, in the backlight, there isan issue that as light absorption by the electrode has wavelengthdependence, chromaticity of illumination light varies with increasingdistance from a light source mounted on an edge of a light guide plate.

The present invention is made to solve the above-described issues, andit is an object of the invention to provide an illumination unit and adisplay which are capable of further uniformizing chromaticity ofillumination light in a plane while suppressing a reduction in lightextraction efficiency.

An illumination unit of the invention includes a first transparentsubstrate and a second transparent substrate disposed to be separatedfrom and face each other and a light source emitting light to an endsurface of the first transparent substrate or the second transparentsubstrate. The illumination unit further includes an electrode disposedon a surface of the first transparent substrate or the secondtransparent substrate and generating an electric field in a directionparallel to the surface of the first transparent substrate, and a lightmodulation layer disposed in a gap between the first transparentsubstrate and the second transparent substrate and exhibiting ascattering property or transparency with respect to light from the lightsource, depending on magnitude of the electric field.

A display of the invention includes a display panel including aplurality of pixels arranged in a matrix and being driven based on animage signal, and an illumination unit illuminating the display panel.The illumination unit included in the display includes the samecomponents as those in the above-described illumination unit.

In the illumination unit and the display of the invention, the electrodeis disposed on only the surface of one of the first transparentsubstrate and the second transparent substrate allowing the lightmodulation layer to be sandwiched therebetween. Therefore, a lightabsorption amount by the electrode when light emitted from the lightsource repeatedly passes through the electrode in the light modulationdevice while propagating through the light guide plate is smaller,compared to the case where the electrodes are disposed on the surfacesof both of the transparent substrates in the light modulation device.Further, as the light absorption amount by the electrode is small, achange in chromaticity of illumination light in a plane is also small.

In the illumination unit and the display of the invention, the electrodemay be configured of a first electrode having comb teeth which extend ina first direction and a second electrode having comb teeth which aredisposed alternately with the comb teeth of the first electrode. Thefirst direction here may be parallel to a side surface facing the lightsource of side surfaces of the first transparent substrate or may beparallel to a normal to a side surface facing the light source of sidesurfaces of the first transparent substrate.

According to the illumination unit and the display of the invention, theelectrode is disposed on only the surface of one of the firsttransparent substrate and the second transparent substrate allowing thelight modulation layer to be sandwiched therebetween; therefore, thelight absorption amount by the electrode and a change in chromaticity ofillumination light in a plane are allowed to be reduced. As a result,chromaticity of illumination light in a plane is allowed to be furtheruniformized while suppressing a reduction in light extractionefficiency.

Additional features and advantages are described herein, and will beapparent from the following Detailed Description and the figures.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a sectional view illustrating an example of a configuration ofa backlight according to a first embodiment of the invention.

FIG. 2 is a perspective view illustrating an example of a configurationof a light source in FIG. 1.

FIG. 3 is a perspective view illustrating an example of a configurationof an electrode in FIG. 1.

FIG. 4 is a perspective view illustrating another example of theconfiguration of the electrode in FIG. 3.

FIG. 5 is a sectional view illustrating another example of theconfiguration of the backlight in FIG. 1.

FIG. 6 is a schematic view for describing a configuration when a voltageis not applied to a light modulation device in FIG. 1.

FIG. 7 is a schematic view for describing a configuration when a voltageis applied to the light modulation device in FIG. 1.

FIG. 8 is a schematic view for describing a function of the backlight inFIG. 1.

FIG. 9 is a sectional view for describing a step of manufacturing thebacklight in FIG. 1.

FIG. 10 is a sectional view for describing a manufacturing stepfollowing FIG. 9.

FIG. 11 is a sectional view for describing a manufacturing stepfollowing FIG. 10.

FIG. 12 is a sectional view illustrating an example of a configurationof a backlight according to a second embodiment of the invention.

FIG. 13 is a schematic view for describing a configuration when avoltage is not applied to a light modulation device in FIG. 12.

FIG. 14 is a schematic view for describing a configuration when avoltage is applied to the light modulation device in FIG. 12.

FIG. 15 is a perspective view illustrating another example of theconfiguration of the electrode in FIG. 1.

FIG. 16 is a perspective view illustrating another example of theconfiguration of the electrode in FIG. 15.

FIG. 17 is a schematic view for describing an example of a configurationwhen a voltage is not applied to the light modulation device in the casewhere the electrode has the configuration illustrated in FIGS. 15 and16.

FIG. 18 is a schematic view for describing an example of a configurationwhen a voltage is applied to the light modulation device in the casewhere the electrode has the configuration illustrated in FIGS. 15 and16.

FIG. 19 is a schematic view for describing another example of theconfiguration when a voltage is not applied to the light modulationdevice in the case where the electrode has the configuration illustratedin FIGS. 15 and 16.

FIG. 20 is a schematic view for describing another example of theconfiguration when a voltage is applied to the light modulation devicein the case where the electrode has the configuration illustrated inFIGS. 15 and 16.

FIG. 21 is a perspective view illustrating a modification of aconfiguration of a light guide plate in FIGS. 1 and 12.

FIG. 22 is a perspective view illustrating another modification of theconfiguration of the light guide plate in FIGS. 1 and 12.

FIG. 23 is a schematic view illustrating a state where light propagatesthrough the light guide plate in FIGS. 21 and 22.

FIG. 24 is a schematic view illustrating a state where light ispartially emitted from the light guide plate in FIGS. 21 and 22.

FIG. 25 is a sectional view illustrating a first modification of theconfiguration of the backlight in FIGS. 1 and 12.

FIG. 26 is a sectional view illustrating a second modification of theconfiguration of the backlight in FIGS. 1 and 12.

FIG. 27 is a sectional view illustrating a third modification of theconfiguration of the backlight in FIGS. 1 and 12.

FIG. 28 is a sectional view illustrating an example of a display as anapplication example.

DETAILED DESCRIPTION

Embodiments of the invention will be described in detail below referringto the accompanying drawings. It is to be noted that description will begiven in the following order.

1. First Embodiment (FIGS. 1 to 11)

An example in which a light modulation device including a horizontalalignment film is disposed in a backlight

2. Second Embodiment (FIGS. 12 to 14)

An example in which a light modulation device including a verticalalignment film is disposed in a backlight.

3. Modifications

An example in which a direction of comb teeth of an electrode isdifferent (FIGS. 15 and 16)

An example in which an alignment state in a light modulation layer isdifferent (FIGS. 17 to 20)

An example in which strip-like projections are formed on a top surfaceof a light guide plate (FIGS. 21 to 24)

An example in which the position of a light modulation device isdifferent (FIGS. 25 to 27)

4. Application Example (FIG. 28)

An example in which a backlight of any of the above-describedembodiments and the like is used as a light source of a display

1. First Embodiment

FIG. 1(A) is a sectional view illustrating an example of a schematicconfiguration of a backlight 1 (an illumination unit) according to afirst embodiment of the invention. FIG. 1(B) is a sectional viewillustrating an example of a specific configuration of the backlight 1in FIG. 1(A). It is to be noted that FIGS. 1(A) and (B) are schematicillustrations, and dimensions and shapes in the illustrations are notnecessarily the same as actual dimensions and shapes. The backlight 1illuminates, for example, a liquid crystal display panel or the likefrom a back side thereof, and includes a light guide plate 10, a lightsource 20 disposed on a side surface of the light guide plate 10, alight modulation device 30 and a reflective plate 40 disposed behind thelight guide plate 10, and a drive circuit 50 driving the light source 20and the light modulation device 30.

The light guide plate 10 guides light from the light source 20 disposedon the side surface of the light guide plate 10 to a top surface of thelight guide plate 10. The light guide plate 10 has a shape correspondingto a display panel (not illustrated) disposed on the top surface of thelight guide plate 10, for example, a rectangular parallelepiped shapesurrounded by a top surface, a bottom surface, and side surfaces. It isto be noted that a side surface where light from the light source 20enters of the side surfaces of the light guide plate 10 is hereinafterreferred to as light incident surface 10A. In the light guide plate 10,one or both of the top surface and the bottom surface have apredetermined patterned shape, and the light guide plate 10 has afunction of scattering and uniformizing light incident from the lightincident surface 10A. It is to be noted that, in the case where avoltage applied to the backlight 1 is modulated to uniformize luminance,a flat light guide plate which is not patterned may be used as the lightguide plate 10. The light guide plate 10 also functions as a supportingbody supporting an optical sheet (for example, a diffuser plate, adiffuser sheet, a lens film, or a polarization splitter sheet) disposedbetween the display panel and the backlight 1. The light guide plate 10is formed by mainly including a transparent thermoplastic resin such asa polycarbonate resin (PC) or an acrylic resin (polymethylmethacrylate(PMMA)).

As illustrated in FIG. 2(A), the light source 20 is configured of alinear light source 21 and a reflective mirror 22. The linear lightsource 21 is configured of, for example, a hot cathode fluorescent lamp(HCFL) or a CCFL. The reflective mirror 22 reflects, to the lightincident surface 10A, light toward a direction not directly entering thelight incident surface 10A in light emitted from the linear light source21. For example, as illustrated in FIG. 2(B) or 2(C), the light source20 may be configured of a plurality of point-like light sources 23arranged in one line. The point-like light sources 23 each emit light tothe light incident surface 10A, and each are configured of, for example,a light-emitting device having a light emission spot on a surface facingthe light incident surface 10A. Examples of such a light-emitting deviceinclude an LED and a laser diode (LD).

For example, as illustrated in FIG. 2(B) or 2(C), every two or morepoint-like light sources 23 in the plurality of point-like light sources23 may be arranged on one common substrate 24. In this case, a lightsource block 25 is configured of one substrate 24 and two or morepoint-like light sources 23 arranged on the substrate 24. The substrate24 is, for example, a circuit board on which wiring electricallyconnecting the point-like light sources 23 and the drive circuit 50 toeach other is installed, and the respective point-like light sources 23are mounted on the circuit board. The respective point-like lightsources 23 arranged on the common substrate 24 (the respectivepoint-like light sources 23 in one light source block 25) arecollectively (not independently) driven by the drive circuit 50, and areconnected to one another in parallel or in series (not illustrated).Moreover, the point-like light sources 23 arranged on differentsubstrates 24 (the point-like light sources 23 in respective lightsource blocks 25) may be collectively (not independently) driven by thedrive circuit 50, and are connected to one another, for example, inparallel as illustrated in FIG. 2(B), or in series (not illustrated).For example, the point-like light sources 23 arranged on differentsubstrates 24 (the point-like light sources 23 in respective lightsource blocks 25) may be driven by the drive circuit 50 independently ofone light source block 25 to another. At this time, for example, asillustrated in FIG. 2(C), the point-like light sources 23 arranged ondifferent substrates 24 (the point-like light sources 23 in respectivelight source blocks 25) are connected to different current paths.

As illustrated in FIGS. 2(A) to 2(C), the light source 20 may bedisposed on only one side surface of the light guide plate 10, oralthough not illustrated, the light sources 20 may be disposed on twoside surfaces, three side surfaces, or all side surfaces of the lightguide plate 10.

The reflective plate 40 returns light leaked from behind the light guideplate 10 through the light modulation device 30 to the light guide plate10, and has, for example, functions such as reflection, diffusion, andscattering. The reflective plate 40 allows light emitted from the lightsource 20 to be efficiently used, and is also useful to improve frontluminance. The reflective plate 40 is made of, for example, foamed PET(polyethylene terephthalate), a silver-evaporated film, a multilayerreflective film, or white PET.

In the embodiment, the light modulation device 30 is in close contactwith a back side (the bottom surface) of the light guide plate 10without an air layer in between, and is bonded to the back side of thelight guide plate 10 with, for example, an adhesive (not illustrated) inbetween. For example, as illustrated in FIG. 1(B), the light modulationdevice 30 is configured by arranging a transparent substrate 31, anelectrode 32, an alignment film 33, a light modulation layer 34, analignment film 35, and a transparent substrate 36 in order from a sidecloser to the reflective plate 40.

The transparent substrates 31 and 36 support the light modulation layer34, and are typically configured of substrates transparent to visiblelight, for example, glass plates or plastic films. The electrode 32 isdisposed on a surface located closer to the light modulation layer 34 ofthe transparent substrate 31, and has a configuration allowing anelectric field to be generated in the light modulation layer 34 in adirection parallel to a surface of the transparent substrate 31. Morespecifically, for example, as illustrated in a part of the lightmodulation device 30 in FIG. 3(A), the electrode 32 includes a firstelectrode 32A having comb teeth which extend in one direction (a firstdirection) in a plane and a second electrode 32B having comb teeth whichare arranged alternately with the comb teeth of the first electrode 32A.For example, as illustrated in FIGS. 3(B) and (C), the comb teeth of thefirst electrode 32A and the second electrode 32B extend in a directionparallel to an extending direction of the light source 20 when the lightsource 20 is disposed close to only one side surface of the lightmodulation device 30 or when the light sources 20 are arranged close totwo side surfaces facing each other of the side surfaces of the lightmodulation device 30.

For example, as illustrated in FIGS. 3(A) to (C), the first electrode32A and the second electrode 32B each may be configured of a singlestructure formed on an entire surface of the transparent substrate 31.Moreover, for example, as illustrated in FIGS. 4(A) to (C), the firstelectrode 32A and the second electrode 32B each may be configured of aplurality of structures (sub-electrodes 32A′ and 32B′). Each of thesub-electrodes 32A′ has comb teeth extending in one direction (the firstdirection) in a plane, and each of the sub-electrodes 32B′ has combteeth arranged alternately with the comb teeth of the sub-electrode32A′. It is to be noted that a pair of the sub-electrodes 32A′ and 32B′engaged in each other is referred to as sub-electrode pair 32C.

A plurality of sub-electrode pairs 32C may be arranged in one directionin a plane, for example, as illustrated in FIGS. 4(A) and (B), or in amatrix, for example, as illustrated in FIG. 4(C). It is to be noted thatan arrangement direction in FIG. 4(A) corresponds to a directionparallel to an extending direction of the light source 20 when the lightsource 20 is disposed on only one side surface of the light guide plate10, or when the light sources 20 are arranged on two side surfacesfacing each other of the side surfaces of the light guide plate 10.Moreover, an arrangement direction in FIG. 4(B) corresponds to adirection orthogonal to the extending direction of the light source 20when the light source 20 is disposed on only one side surface of thelight guide plate 10, or when the light sources 20 are arranged on twoside surfaces facing each other of the side surfaces of the light guideplate 10. Further, an arrangement direction in FIG. 4(C) corresponds totwo directions including a direction parallel to the extending directionof the light source 20 and the direction orthogonal to the extendingdirection of the light source 20 when the light source 20 is disposed ononly one side surface of the light guide plate 10, or when the lightsources 20 are arranged on two side surfaces facing each other of theside surfaces of the light guide plate 10.

The electrode 32 is made of a transparent conductive material, forexample, indium tin oxide (ITO). However, the electrode 32 may not bemade of a transparent material, and may be made of, for example, metal.It is to be noted that when the electrode 32 is made of metal, theelectrode 32 also has a function of reflecting light entering the lightmodulation device 30 from behind the light guide plate 10 as in the caseof the reflective plate 40. Therefore, in this case, for example, asillustrated in FIG. 5, the reflective plate 40 may not be included.

In the case where the first electrode 32A and the second electrode 32Bare configured of a plurality of sub-electrodes 32A′ and 32B′,respectively, portions facing the sub-electrode pairs 32C of the lightmodulation device 30 when the sub-electrode pairs 32C are viewed from adirection of a normal to the light modulation device 30 configure lightmodulation cells 30S. For example, a portion indicated by a broken linein FIG. 1(B) configures the light modulation cell 30S. The lightmodulation cells 30S are allowed to be separately and independentlydriven by applying a predetermined voltage to the sub-electrodes 32A′and 32B′, and exhibit transparency or a scattering property with respectto light from the light source 20, depending on a voltage value appliedto the sub-electrodes 32A′ and 32B′. It is to be noted that transparencyand the scattering property will be described in more detail when thelight modulation layer 34 is described.

The alignment films 33 and 35 align, for example, a liquid crystal or amonomer used in the light modulation layer 34. Kinds of alignment filmsinclude a vertical alignment film and a horizontal alignment film, andin the embodiment, horizontal alignment films are used as the alignmentfilms 33 and 35. Examples of the horizontal alignment films include analignment film formed by performing a rubbing process on polyimide,polyamide imide, polyvinyl alcohol, or the like, and an alignment filmprovided with a groove by transfer or etching. Other examples of thehorizontal alignment films include an alignment film formed by obliquelyevaporating an inorganic material such as silicon oxide, a diamond-likecarbon alignment film formed by ion beam irradiation, and an alignmentfilm provided with an electrode pattern slit. In the case where plasticfilms are used as the transparent substrates 31 and 36, in amanufacturing process, polyamide imide capable of forming a film at atemperature of 100° C. or less is preferably used for the alignmentfilms 33 and 35, because a firing temperature after coating surfaces ofthe transparent substrates 31 and 36 with the alignment films 33 and 35is preferably as low as possible.

Moreover, it is only necessary for both of vertical and horizontalalignment films to have a function of aligning a liquid crystal and amonomer, and reliability, which is necessary for a typical liquidcrystal display, with respect to repeated voltage application is notnecessary. It is because reliability with respect to voltage applicationafter forming a device is determined by an interface between a resultantformed by polymerizing a monomer, and a liquid crystal. Moreover, evenif the alignment films 33 and 35 are not used, for example, when anelectric field or a magnetic field is applied between the firstelectrode 32A and the second electrode 32B (or the sub-electrodes 32A′and 32B′), a liquid crystal or a monomer used in the light modulationlayer 34 is allowed to be aligned. In other words, while an electricfield or a magnetic field is applied between the first electrode 32A andthe second electrode 32B (or the sub-electrodes 32A′ and 32B′), thealignment state of the liquid crystal or the monomer under voltageapplication is allowed to be fixed by ultraviolet irradiation. In thecase where a voltage is used to form the alignment films 33 and 35, anelectrode for alignment and an electrode for drive may be separatelyformed, or as a liquid crystal material, a dual-frequency liquid crystalallowing the sign of dielectric constant anisotropy to be inverted by afrequency may be used. Moreover, in the case where a magnetic field isused to form the alignment films 33 and 35, for the alignment films 33and 35, a material with large magnetic susceptibility anisotropy ispreferably used, and, for example, a material with a large number ofbenzene rings is preferably used.

The light modulation layer 34 exhibits a scattering property ortransparency with respect to light from the light source 20 depending onmagnitude of an electric field. More specifically, the light modulationlayer 34 exhibits transparency with respect to light from the lightsource 20 when a voltage is not applied to the electrode 32 and exhibitsthe scattering property when a voltage is applied to the electrode 32.For example, as illustrated in FIG. 1(B), the light modulation layer 34is a composite layer including a bulk 34A and a plurality ofmicroparticles 34B dispersed in the bulk 34A. The bulk 34A and themicroparticles 34B have optical anisotropy.

FIG. 6 schematically illustrates an example of an alignment state in thebulk 34A and the microparticles 34B when a voltage is not appliedbetween the first electrode 32A and the second electrode 32B (or thesub-electrodes 32A′ and 32B′). An ellipsoid 134A in FIG. 6 is an exampleof a refractive index ellipsoid exhibiting refractive index anisotropyof the bulk 34A when a voltage is not applied between the firstelectrode 32A and the second electrode 32B (or the sub-electrodes 32A′and 32B′). An ellipsoid 134B in FIG. 6 is an example of a refractiveindex ellipsoid exhibiting refractive index anisotropy of themicroparticle 34B when a voltage is not applied between the firstelectrode 32A and the second electrode 32B (or the sub-electrodes 32A′and 32B′). The refractive index ellipsoid is a tensor ellipsoidrepresenting a refractive index of linearly polarized light incidentfrom various directions, and when a section of an ellipsoid from a lightincident direction is observed, the refractive index is allowed to begeometrically learned.

FIG. 7 schematically illustrates an example of an alignment state in thebulk 34A and the microparticles 34B when a voltage is applied betweenthe first electrode 32A and the second electrode 32B (or thesub-electrodes 32A′ and 32B′). An ellipsoid 134A in FIG. 7 is an exampleof a refractive index ellipsoid exhibiting refractive index anisotropyof the bulk 34A when a voltage is applied between the first electrode32A and the second electrode 32B (or the sub-electrodes 32A′ and 32B′).An ellipsoid 134B in FIG. 7 is an example of a refractive indexellipsoid exhibiting refractive index anisotropy of the microparticle34B when a voltage is applied between the first electrode 32A and thesecond electrode 32B (or the sub-electrodes 32A′ and 32B′).

For example, as illustrated in FIG. 6, the bulk 34A and themicroparticle 34B are structured to allow the direction of an opticalaxis AX1 of the bulk 34A (a long axis of the ellipsoid 134A) and thedirection of an optical axis AX2 of the microparticle 34B (a long axisof the ellipsoid 134B) to coincide with (be parallel to) each other whena voltage is not applied between the first electrode 32A and the secondelectrode 32B (or the sub-electrodes 32A′ and 32B′). It is to be notedthat the optical axes AX1 and AX2 each indicate a line parallel to atravel direction of a light beam allowing a refractive index to have onevalue irrespective of polarization direction. Moreover, it is notnecessary for the directions of the optical axis AX1 and the opticalaxis AX2 to consistently coincide with each other when a voltage is notapplied between the first electrode 32A and the second electrode 32B (orthe sub-electrodes 32A′ and 32B′), and the directions of the opticalaxis AX1 and the optical axis AX2 may be slightly deviated from eachother due to, for example, a manufacturing error.

Moreover, the optical axis AX2 is parallel to the light incident surface10A of the light guide plate 10 as well as parallel to a surface of thetransparent substrate 31 when a voltage is not applied between the firstelectrode 32A and the second electrode 32B (or the sub-electrodes 32A′and 32B′). In other words, when a voltage is not applied between thefirst electrode 32A and the second electrode 32B (or the sub-electrodes32A′ and 32B′), the optical axis AX2 is parallel to a plane includingthe first electrode 32A and the second electrode 32B (or thesub-electrodes 32A′ and 32B′) as well as parallel to an extendingdirection of comb teeth of the first electrode 32A and the secondelectrode 32B (or the sub-electrodes 32A′ and 32B′).

On the other hand, the bulk 34A is structured to have a fixed opticalaxis AX1 irrespective of whether or not a voltage is applied between thefirst electrode 32A and the second electrode 32B (or the sub-electrodes32A′ and 32B′). More specifically, the optical axis AX1 is parallel tothe light incident surface 10A of the light guide plate 10 as well asparallel to the surface of the transparent substrate 31. In other words,when a voltage is not applied between the first electrode 32A and thesecond electrode 32B (or the sub-electrodes 32A′ and 32B′), the opticalaxis AX1 is parallel to the optical axis AX2.

It is to be noted that it is not necessary for the optical axis AX2 tobe consistently parallel to the light incident surface 10A of the lightguide plate 10 as well as the surface of the transparent substrate 31,and the optical axis AX2 may be aligned in a direction intersecting withone or both of the light incident surface 10A and the surface of thetransparent substrate 31 at a small angle due to, for example, amanufacturing error.

In this case, ordinary refractive indices of the bulk 34A and themicroparticle 34B are preferably equal to each other, and extraordinaryrefractive indices of the bulk 34A and the microparticle 34B arepreferably equal to each other. In this case, for example, when avoltage is not applied between the first electrode 32A and the secondelectrode 32B (or the sub-electrodes 32A′ and 32B′), there is littledifference in refractive index in all directions including a frontdirection and an oblique direction, and high transparency is obtained.Therefore, light toward the front direction and light toward the obliquedirection pass through the light modulation layer 34 without beingscattered in the light modulation layer 34. As a result, for example, asillustrated in FIGS. 8(A) and (B), light L from the light source 20(light from the oblique direction) is totally reflected by an interface(an interface between the transparent substrate 31 or the light guideplate 10 and air) of a transparent region (a transmission region 30A) ofthe light modulation device 30, and luminance (luminance in blackdisplay) in the transmission region 30A is decreased, compared to thecase where the light modulation device 30 is not included (indicated byan alternate long and short dash line in FIG. 8(B)). It is to be notedthat a graph in FIG. 8(B) is obtained by measuring front luminance in astate where a diffuser sheet 41 is disposed on the light guide plate 10as illustrated in FIG. 8(A).

Moreover, for example, as illustrated in FIG. 7, the bulk 34A and themicroparticles 34B are structured to allow directions of the opticalaxes AX1 and AX2 to be different from (intersect with or be orthogonalto) each other when a voltage is applied between the first electrode 32Aand the second electrode 32B (or the sub-electrodes 32A′ and 32B′).Further, for example, the microparticles 34B are structured to allow theoptical axis AX2 to be parallel to the normal to the light incidentsurface 10A of the light guide plate 10 as well as parallel to thesurface of the transparent substrate 31 when a voltage is appliedbetween the first electrode 32A and the second electrode 32B (or thesub-electrodes 32A′ and 32B′). In other words, when a voltage is appliedbetween the first electrode 32A and the second electrode 32B (or thesub-electrodes 32A′ and 32B′), the optical axis AX2 is parallel to aplane including the first electrode 32A and the second electrode 32B (orthe sub-electrodes 32A′ and 32B′) and intersects with (or is orthogonalto) an extending direction of comb teeth of the sub-electrodes 32A′ and32B′.

Therefore, when a voltage is applied between the first electrode 32A andthe second electrode 32B (or the sub-electrodes 32A′ and 32B′), in thelight modulation layer 34, a difference in refractive index in alldirections in a plane parallel to the surface of the transparentsubstrate 31 is increased to obtain a high scattering property.Accordingly, for example, light toward the front direction and lighttoward the oblique direction are scattered in the light modulation layer34. As a result, for example, as illustrated in FIGS. 8(A) and (B), thelight L from the light source 20 (light from the oblique direction)passes through an interface (an interface between the transparentsubstrate 31 or the light guide plate 10 and the air) of a region in ascattering state (a scattering region 30B) in the light modulationdevice 30, and light having passed toward the reflective plate 40 isreflected by the reflective plate 40 to pass through the lightmodulation device 30. Therefore, the luminance of the scattering region30B is extremely higher than that in the case where the light modulationdevice 30 is not included (indicated by an alternate long and short dashline in FIG. 8(B)), and luminance in white display is partiallyincreased (partial luminance enhancement) by a reduced amount of theluminance of the transmission region 30A.

It is to be noted that the ordinary refractive indices of the bulk 34Aand the microparticle 34B may be slightly different from each other dueto, for example, a manufacturing error, and are preferably, for example,0.1 or less, and more preferably 0.05 or less. Moreover, theextraordinary refractive indices of the bulk 34A and the microparticle34B may be slightly different from each other due to, for example, amanufacturing error, and are preferably, for example, 0.1 or less, andmore preferably 0.05 or less.

Moreover, a refractive index difference (=extraordinary refractiveindex−ordinary refractive index) in the bulk 34A and a refractive indexdifference (=extraordinary refractive index−ordinary refractive index)in the microparticle 34B are preferably as large as possible, and arepreferably 0.05 or over, more preferably 0.1 or over, and still morepreferably 0.15 or over. In the case where the refractive indexdifferences in the bulk 34A and the microparticle 34B are large, thescattering power of the light modulation layer 34 is enhanced to allowlight guide conditions to be easily disrupted, thereby allowing lightfrom the light guide plate 10 to be easily extracted.

Further, the bulk 34A and the microparticle 34B have different responsespeeds with respect to an electric field. The bulk 34A has, for example,a streaky structure or a porous structure which does not respond to anelectric field, or a rod-like structure having a response speed slowerthan that of the microparticle 34B. The bulk 34A is formed of, forexample, a polymer material obtained by polymerizing a low-molecularmonomer. The bulk 34A is formed, for example, by polymerizing, by one orboth of heat and light, a material (for example, a monomer) withorientation and polymerization which is aligned along the alignmentdirection of the microparticles 34B or the alignment directions of thealignment films 33 and 35.

On the other hand, the microparticles 34B mainly include, for example, aliquid crystal material, and have a response speed sufficiently higherthan that of the bulk 34A. Examples of the liquid crystal material(liquid crystal molecules) included in the microparticles 34B includerod-like molecules. As liquid crystal molecules included in themicroparticles 34B, liquid crystal molecules having positive dielectricconstant anisotropy (a so-called positive type liquid crystal) arepreferably used.

In this case, when a voltage is not applied between the first electrode32A and the second electrode 32B (or the sub-electrodes 32A′ and 32B′),the long-axis directions of the liquid crystal molecules in themicroparticles 34B are parallel to the optical axis AX1. At this time,the long axes of the liquid crystal molecules in the microparticles 34Bare parallel to the light incident surface 10A of the light guide plate10 as well as parallel to the surface of the transparent substrate 31.Moreover, when a voltage is applied between the first electrode 32A andthe second electrode 32B (or the sub-electrodes 32A′ and 32B′), thelong-axis directions of the liquid crystal molecules in themicroparticles 34B intersect with (or is orthogonal to) the optical axisAX1. At this time, the long axes of the liquid crystal molecules in themicroparticles 34B are parallel to the normal to the light incidentsurface 10A of the light guide plate 10 as well as parallel to thesurface of the transparent substrate 31.

The above-described monomer having orientation and polymerization may bea material having optical anisotropy and forming a composite materialwith a liquid crystal; however, a low-molecular monomer which is curedwith ultraviolet light is preferable in this embodiment. It ispreferable that, in a state where no voltage is applied, directions ofoptical anisotropy of the liquid crystal and a resultant (a polymermaterial) formed by polymerizing a low-molecular monomer coincide witheach other; therefore, before curing the low-molecular monomer withultraviolet light, the liquid crystal and the low-molecular monomer arepreferably aligned in the same direction. In the case where a liquidcrystal is used as the microparticles 34B, when the liquid crystalincludes rod-like molecules, the used monomer material preferably has arod-like shape. As described above, a material having both ofpolymerization and liquid crystal properties is preferably used as themonomer material, and, for example, the monomer material preferablyincludes one or more functional groups selected from the groupconsisting of an acrylate group, a methacrylate group, an acryloyloxygroup, a methacryloyloxy group, a vinyl ether group, and an epoxy groupas polymerizable functional groups. These functional groups are allowedto be polymerized by ultraviolet, infrared, or electron irradiation, orby heating. To suppress a reduction in the degree of alignment underultraviolet irradiation, a liquid crystal material having apolyfuncitonal group may be added. In the case where the bulk 34A hasthe above-described streaky structure, as the material of the bulk 34A,a bifunctional liquid crystal monomer is preferably used. Moreover, amonofunctional monomer may be added to the material of the bulk 34A toadjust a temperature at which liquid crystal properties are exhibited,or a tri- or more-functional monomer may be added to the material of thebulk 34A to improve crosslink density.

For example, the drive circuit 50 controls the magnitude of a voltageapplied to the first electrode 32A and the second electrode 32B (or thesub-electrodes 32A′ and 32B′) to allow the optical axes AX2 of themicroparticles 34B in one light modulation cell 30S to be parallel orsubstantially parallel to the optical axis AX1 of the bulk 34A, as wellas to allow the optical axes AX2 of the microparticles 34B in anotherlight modulation cell 30S to intersect with or be orthogonal to theoptical axis AX1 of the bulk 34A. In other words, the drive circuit 50allows, by electric field control, the direction of the optical axis AX1of the bulk 34A and the directions of the optical axes AX2 of themicroparticles 34B to coincide with (or substantially coincide with)each other or to be different from (or orthogonal to) each other.

Moreover, for example, when the electrode 32 is configured of aplurality of sub-electrode pairs 32C and the sub-electrode pairs 32C arearranged in a direction parallel to the normal to the light incidentsurface 10A, the drive circuit 50 applies, to the sub-electrode pairs32C, a voltage with a peak value, a duty ratio, and a frequency one ormore of which are modulated according to a distance from the lightsource 20 to the sub-electrode pairs 32C. For example, the voltage ismodulated to enhance the scattering property of the light modulationcell 30S with increasing distance from the light source 20. Further, thedrive circuit 50 may apply, to the sub-electrode pairs 32C, a voltagewith the peak value, the duty ratio, and the frequency one or more ofwhich are modulated with consideration given to not only the distancefrom the light source 20 but also an externally supplied image signal.

Moreover, for example, when the light source 20 is configured of aplurality of light source blocks 25 capable of being drivenindependently of each other, the drive circuit 50 may apply, torespective light source blocks 25, a voltage or a current with a peakvalue, a duty ratio, and a frequency one of which is modulated accordingto a distance from the light source 20 to a sub-electrode pair 32C towhich a voltage is to be applied and an externally supplied imagesignal.

Next, a method of manufacturing the backlight 1 according to theembodiment will be described below referring to FIGS. 9(A) to (C) toFIGS. 11(A) to (C).

First, a transparent conductive film 32D made of ITO or the like isformed on the transparent substrate 31 configured of a glass substrateor a plastic film substrate (refer to FIG. 9(A)). Next, a patternedresist layer (not illustrated) is formed on the transparent conductivefilm 32D, and then the transparent conductive film 32D is selectivelyetched with use of the resist layer as a mask. As a result, theelectrode 32 is formed (refer to FIG. 9(B)).

Next, after an entire surface of the transparent substrate 31 is coatedwith the alignment film 33, the alignment film 33 is dried and fired(refer to FIG. 9(C)). In the case where a polyimide-based material isused as the alignment film 33, NMP (N-methyl-2-pyrrolidone) is oftenused as a solvent; however, at this time, a temperature of approximately200° C. is necessary under an atmosphere. It is to be noted that, inthis case, when a plastic substrate is used as the transparent substrate31, the alignment film 33 may be vacuum-dried and fired at 100° C. Afterthat, a rubbing process is performed on the alignment film 33.Therefore, the alignment film 33 functions as an alignment film forhorizontal alignment.

Next, spacers 38 allowing a cell gap to be formed are sprayed on thealignment film 33 by a dry method or a wet method (refer to FIG. 10(A)).It is to be noted that, in the case where the light modulation cells 30Sare formed by a vacuum bonding method, the spacers 38 may be mixed in amixture which is to be dropped. Alternatively, columnar spacers may beformed by a photolithography method, instead of the spacers 38.

Then, the alignment film 35 formed by a method similar to theabove-described method is coated with a sealant pattern 39 for bondingand preventing leakage of the liquid crystal in, for example, a frameshape (refer to FIG. 10(B)). The sealant pattern 39 is allowed to beformed by a dispenser method or a screen printing method.

The vacuum bonding method (a one-drop-fill (ODF) method) will bedescribed below; however, the light modulation cells 30S may also beformed by a vacuum injection method, a roll bonding method, or the like.

First, a mixture 42 of a liquid crystal and a monomer, corresponding toa volume determined by a cell gap, a cell area, or the like, is droppeduniformly on a plane (refer to FIG. 10(C)). The mixture 42 is preferablydropped with use of a linear guide precise dispenser; however, a diecoater or the like may be used with use of the sealant pattern 39 as abank.

The above-described materials may be used as the liquid crystal and themonomer, and a weight ratio of the liquid crystal to the monomer iswithin a range of 98:2 to 50:50, preferably within a range of 95:5 to75:25, and more preferably within a range of 92:8 to 85:15. A drivevoltage is allowed to be decreased by increasing the ratio of the liquidcrystal; however, when the liquid crystal is increased too much, theliquid crystal tends to have difficulty in returning to a transparentstate, such as a reduction in whiteness under voltage application or adecrease in the response speed after turning the voltage off.

In addition to the liquid crystal and the monomer, a polymerizationinitiator is added to the mixture 42. A monomer ratio of the addedpolymerization initiator is adjusted within a range of 0.1 to 10 wt %,depending on a used ultraviolet wavelength. A polymerization inhibitor,a plasticizer, a viscosity modifier, or the like may be further added tothe mixture 42, as necessary. When the monomer is a solid or gel at roomtemperature, a cap, a syringe, and a substrate are preferably warmed.

After the transparent substrates 31 and 36 are put in a vacuum bondingsystem (not illustrated), evacuation is performed to bond thetransparent substrates 31 and 36 (refer to FIG. 11(A)). After that, aresultant is released to the atmosphere to uniformize the cell gap byuniform pressurization under atmospheric pressure. The cell gap may beappropriately selected based on a relationship between white luminance(whiteness) and the drive voltage; however, the cell gap is within arange of 5 to 40 μm, preferably within a range of 6 to 20 μm, and morepreferably within a range of 7 to 10 μm.

After bonding, an alignment process is preferably performed as necessary(not illustrated). In the case where light leakage occurs by aninsertion of a bonded cell between crossed-Nicols polarizers, the cellmay be heated for a predetermined time or be left at room temperature tobe aligned. After that, the monomer is irradiated with ultraviolet lightL3 to be polymerized (refer to FIG. 11(B)). Thus, the light modulationdevice 30 is manufactured.

It is preferable to prevent the temperature of the cell from beingchanged under ultraviolet irradiation. An infrared cut filter ispreferably used, or an UV-LED or the like is preferably used as a lightsource. Ultraviolet irradiance exerts an influence on an organizationstructure of a composite material; therefore, the ultraviolet irradianceis preferably adjusted appropriately based on a used liquid crystalmaterial or a used monomer material, and a composition thereof, and theultraviolet irradiance is preferably within a range of 0.1 to 500mW/cm², and more preferably within a range of 0.5 to 30 mW/cm². There isa tendency that the lower the ultraviolet irradiance is, the lower thedrive voltage becomes, and preferable ultraviolet irradiance is allowedto be selected in terms of both of productivity and properties.

Then, the light modulation device 30 is bonded to the light guide plate10 (refer to FIG. 11(C)). Bonding may be carried out by sticking oradhesion; however, it is preferable that the light modulation device 30be adhered or stuck with a material having a refractive index which isas close to a refractive index of the light guide plate 10 and arefractive index of a substrate material of the light modulation device30 as possible. Finally, leading lines (not illustrated) are attached tothe electrode 32. Thus, the backlight 1 according to the embodiment ismanufactured.

Although the process of forming the light modulation device 30, andfinally bonding the light modulation device 30 to the light guide plate10 is described, the transparent substrate 36 on which the alignmentfilm 35 is formed may be bonded in advance to the surface of the lightguide plate 10 to form the backlight 1. Moreover, the backlight 1 may beformed by one of a sheet-feeding method and a roll-to-roll method.

Next, functions and effects of the backlight 1 according to theembodiment will be described below.

In the backlight 1 according to the embodiment, a voltage is appliedbetween the sub-electrodes 32A′ and 3B′ of respective light modulationcells 30S to allow the optical axes AX2 of the microparticles 34B in onelight modulation cell 30S to be parallel or substantially parallel tothe optical axis AX1 of the bulk 34A, and to allow the optical axes AX2of the microparticles 34B in another light modulation cell 30S tointersect with or be orthogonal to the optical axis AX1 of the bulk 34A.As a result, light emitted from the light source 20 and entering intothe light guide plate 10 passes through the transmission region 30Awhere the optical axes AX1 and AX2 are parallel or substantiallyparallel to each other of the light modulation device 30. On the otherhand, light emitted from the light source 20 and entering into the lightguide plate 10 is scattered in the scattering region 30B where theoptical axes AX1 and AX2 intersect with or are orthogonal to each otherof the light modulation device 30. Light having passed through a bottomsurface of the scattering region 30B in the scattered light is reflectedby the reflective plate 40 to be returned to the light guide plate 10again, and then the light is emitted from a top surface of the backlight1. Moreover, light toward a top surface of the scattering region 30B inthe scattered light passes through the light guide plate 10, and then isemitted from the top surface of the backlight 1. Thus, in theembodiment, light is hardly emitted from the top surface of thetransmission region 30A, and light is emitted from the top surface ofthe scattering region 30B. Accordingly, a modulation ratio in a frontdirection is increased.

Typically, PDLC is a composite layer which is formed by mixing theliquid crystal material and an isotropic low-molecular material, andcausing phase separation by ultraviolet irradiation, drying of asolvent, or the like, and has microparticles of the liquid crystalmaterial dispersed in a polymer material. The liquid crystal material inthe composite layer is aligned in random directions under no voltageapplication, and thus exhibits the scattering property, but on the otherhand, under voltage application, the liquid crystal material is alignedin an electric field direction; therefore, in the case where theordinary refractive index of the liquid crystal material and therefractive index of the polymer material are equal to each other, theliquid crystal material exhibits high transparency in the frontdirection (in a direction of a normal to the PDLC). However, in thisliquid crystal material, a difference between the extraordinaryrefractive index of the liquid crystal material and the refractive indexof the polymer material becomes pronounced in an oblique direction;therefore, even if the liquid crystal material has transparency in thefront direction, the liquid crystal material exhibits the scatteringproperty in the oblique direction.

A typical light modulation device using the PDLC often has aconfiguration in which the PDLC is sandwiched between two glass plateson which transparent conductive films are formed. When light obliquelyenters from air into the light modulation device with theabove-described configuration, the light incident from the obliquedirection is refracted by a refractive index difference between the airand the glass plate to enter into the PDLC at a smaller angle.Therefore, large scattering does not occur in such a light modulationdevice. For example, when light enters from air at an angle of 80°, theincident angle of the light to the PDLC is reduced to approximately 40°by refraction at a glass interface.

However, in an edge-light system with use of a light guide plate, aslight enters through the light guide plate, the light crosses the PDLCat a large angle of approximately 80°. Accordingly, a difference betweenthe extraordinary refractive index of the liquid crystal material andthe refractive index of the polymer material is large, and light crossesthe PDCL at a larger angle, thereby causing a longer optical pathsubjected to scattering. For example, in the case where microparticlesof a liquid crystal material having an ordinary refractive index of 1.5and an extraordinary refractive index of 1.65 are dispersed in a polymermaterial having a refractive index of 1.5, there is no refractive indexdifference in the front direction (the direction of the normal to thePDLC), but the refractive index difference is large in the obliquedirection. Therefore, the scattering property in the oblique directionis not allowed to be reduced, thereby causing low view anglecharacteristics. Further, in the case where an optical film such as adiffuser film is disposed on the light guide plate, oblique leak lightis diffused also in the front direction by the diffuser film or thelike, thereby causing an increase in light leakage in the frontdirection and a decrease in a modulation ratio in the front direction.

On the other hand, in the embodiment, as the bulk 34A and themicroparticles 34B each include mainly an optical anisotropic material,the scattering property in an oblique direction is reduced, therebyenabling to improve transparency. For example, when the bulk 34A and themicroparticles 34B include mainly the optical anisotropic materials withordinary refractive indices which are equal to each other andextraordinary refractive indices which are also equal to each other, thedirections of the optical axes of the bulk 34A and the microparticles34B coincide with or substantially coincide with each other in a regionwhere a voltage is not applied between the sub-electrodes 32A′ and 32B′.Therefore, the refractive index difference is reduced or eliminated inall directions including the front direction (a direction of the normalto the light modulation device 30) and the oblique direction, therebyobtaining high transparency. As a result, the leakage of light in arange having a large view angle is allowed to be reduced orsubstantially eliminated, and view angle characteristics are allowed tobe improved.

For example, when a liquid crystal having an ordinary refractive indexof 1.5 and an extraordinary refractive index of 1.65, and a liquidcrystal monomer having an ordinary refractive index of 1.5 and anextraordinary refractive index of 1.65 are mixed, and the liquid crystalmonomer is polymerized in a state where the liquid crystal and theliquid crystal monomer are aligned by an alignment film or an electricfield, the optical axis of the liquid crystal and the optical axis of apolymer formed by polymerizing the liquid crystal monomer coincide witheach other. Therefore, the refractive indices are allowed to coincidewith each other in all directions, thereby enabling to achieve a statewhere transparency is high, and to further improve the view anglecharacteristics.

Moreover, in the embodiment, for example, as illustrated in FIGS. 8(A)and (B), luminance in the transmission region 30A (luminance in blackdisplay) is lower, compared to the case where the light modulationdevice 30 is not included (indicated by the alternate long and shortdash line in FIG. 8(B)). On the other hand, luminance in the scatteringregion 30B is significantly increased, compared to the case where thelight modulation device 30 is not included (indicated by the alternatelong and short dash line in FIG. 8(B)), and luminance in white displayis partially increased (partial luminance enhancement) by a reducedamount of the luminance of the transmission region 30A.

The partial luminance enhancement is a technique of enhancing luminancewhen white display is partially performed, compared to the case wherewhite display is performed on an entire screen. The partial luminanceenhancement is generally used in a CRT, a PDP, or the like. However, ina liquid crystal display, as a backlight uniformly emits light in anentire surface thereof irrespective of an image, the luminance is notallowed to be partially enhanced. When an LED backlight in which aplurality of LEDs are two-dimensionally arranged is used as thebacklight, some of the LEDs are allowed to be turned off. However, insuch a case, diffusion light from dark regions in which the LEDs areturned off disappears; therefore, the luminance becomes lower, comparedto the case where all of the LEDs are turned on. Also, the luminance maybe increased by increasing a current applied to some LEDs which areturned on; however, in such a case, a large current flows for anextremely short time, thereby causing an issue in terms of load andreliability of a circuit.

On the other hand, in the embodiment, as the bulk 34A and themicroparticles 34B each include mainly the optical anisotropic material,the scattering property in the oblique direction is suppressed to reduceleak light from the light guide plate in a dark state. Therefore, aslight is guided from a part in a partially-dark state to a part in apartially-bright state, partial luminance enhancement is achievablewithout increasing electric power supplied to the backlight 1.

Moreover, in the embodiment, the electrode 32 is disposed on only thesurface of the transparent substrate 31 in the pair of transparentsubstrates 31 and 36 which allow the light modulation layer 34 to besandwiched therebetween. Therefore, for example, in the case where theelectrode 32 is configured of an ITO film, a light absorption amount bythe electrode 32 when light emitted from the light source 20 repeatedlypasses through the electrode 32 in the light modulation device 30 whilepropagating through the light guide plate 10 is smaller, compared to thecase where the electrodes are disposed on the surfaces of both of thetransparent substrates 31 and 36 in the light modulation device 30.Further, as the light absorption amount by the electrode 32 is small, achange in chromaticity of illumination light in a plane is also small.As a result, chromaticity of illumination light is allowed to be furtheruniformized in a plane while suppressing a reduction in light extractionefficiency.

2. Second Embodiment

FIG. 12(A) is a sectional view illustrating an example of a schematicconfiguration of a backlight 2 (an illumination unit) according to asecond embodiment of the invention. FIG. 12(B) is a sectional viewillustrating an example of a specific configuration of the backlight 2in FIG. 12(A). It is to be noted that FIGS. 12(A) and (B) are schematicillustrations, and dimensions and shapes in the illustrations are notnecessarily the same as actual dimensions and shapes.

The backlight 2 according to the embodiment is distinguished from thebacklight 1 according to the above-described first embodiment andmodifications thereof by the fact that a light modulation device 60 isincluded instead of the light modulation device 30. Description will begiven of, mainly, points different from the above-described embodiment,and points common to the above-described embodiment will not be furtherdescribed.

In the embodiment, the light modulation device 60 is in close contactwith a back side (the bottom surface) of the light guide plate 10without an air layer in between, and is bonded to the back side of thelight guide plate 10 with, for example, an adhesive (not illustrated) inbetween. For example, as illustrated in FIG. 12(B), the light modulationdevice 60 is configured by arranging the transparent substrate 31, theelectrode 32, an alignment film 63, a light modulation layer 64, analignment film 65, and the transparent substrate 36 in order from a sidecloser to the reflective plate 40.

The alignment films 63 and 65 align, for example, a liquid crystal or amonomer used in the light modulation layer 64. Kinds of alignment filmsinclude a vertical alignment film and a horizontal alignment film, andin the embodiment, vertical alignment films are used as the alignmentfilms 63 and 65. The vertical alignment films may be made of a silanecoupling material, polyvinyl alcohol (PVA), a polyimide-based material,a surfactant, or the like. Moreover, when plastic films are used as thetransparent substrates 31 and 36, it is preferable that in amanufacturing process, a firing temperature after coating the surfacesof the transparent substrates 31 and 36 with the alignment films 63 and65 be as low as possible; therefore, a silane coupling material capableof using an alcohol-based solvent is preferably used as the alignmentfilms 63 and 65.

It is to be noted that as the vertical alignment films, verticalalignment films having a function of providing a pretilt to liquidcrystal molecules in contact therewith may be used. Examples of a methodof developing a pretilt function in the vertical alignment film includerubbing. The above-described vertical alignment films may have, forexample, a function of allowing long axes of liquid crystal molecules inproximity to the vertical alignment film to intersect with a normal tothe vertical alignment film at a slight angle.

However, when the vertical alignment films are used as the alignmentfilms 63 and 65, as liquid crystal molecules included in microparticles64B which will be described later, liquid crystal molecules havingnegative dielectric constant anisotropy (a so-called negative typeliquid crystal) are used in some cases, but in the embodiment, liquidcrystal molecules having positive dielectric constant anisotropy (aso-called positive type liquid crystal) are used.

Next, the light modulation layer 64 in the embodiment will be describedbelow. For example, as illustrated in FIG. 12(B), the light modulationlayer 64 is a composite layer including a bulk 64A and a plurality ofmicroparticles 64B dispersed in the bulk 64A. The bulk 64A and themicroparticles 64B have optical anisotropy.

FIG. 13 schematically illustrates an example of an alignment state inthe bulk 64A and the microparticles 64B when a voltage is not appliedbetween the first electrode 32A and the second electrode 32B (or thesub-electrodes 32A′ and 32B′). An ellipsoid 164A in FIG. 13 representsan example of a refractive index ellipsoid exhibiting refractive indexanisotropy of the bulk 64A when a voltage is not applied between thefirst electrode 32A and the second electrode 32B (or the sub-electrodes32A′ and 32B′). An ellipsoid 164B in FIG. 13 represents an example of arefractive index ellipsoid exhibiting refractive index anisotropy of themicroparticle 64B when a voltage is not applied between the firstelectrode 32A and the second electrode 32B (or the sub-electrodes 32A′and 32B′).

FIG. 14 schematically illustrates an example of an alignment state inthe bulk 64A and the microparticles 64B when a voltage is appliedbetween the first electrode 32A and the second electrode 32B (or thesub-electrodes 32A′ and 32B′). An ellipsoid 164A in FIG. 14 representsan example of a refractive index ellipsoid exhibiting refractive indexanisotropy of the bulk 64A when a voltage is applied between the firstelectrode 32A and the second electrode 32B (or the sub-electrodes 32A′and 32B′). An ellipsoid 164B in FIG. 14 represents an example of arefractive index ellipsoid exhibiting refractive index anisotropy of themicroparticle 64B when a voltage is applied between the first electrode32A and the second electrode 32B (or the sub-electrodes 32A′ and 32B′).

For example, as illustrated in FIG. 13, the bulk 64A and themicroparticle 64B are structured to allow the direction of an opticalaxis AX3 of the bulk 64A (a long axis of the ellipsoid 164A) and thedirection of an optical axis AX4 of the microparticle 64B (a long axisof the ellipsoid 164B) to coincide with (be parallel to) each other whena voltage is not applied between the first electrode 32A and the secondelectrode 32B (or the sub-electrodes 32A′ and 32B′). It is to be notedthat the optical axes AX3 and AX4 each indicate a line parallel to atravel direction of a light beam allowing a refractive index to have onevalue irrespective of polarization direction. Moreover, it is notnecessary for the directions of the optical axis AX3 and the opticalaxis AX4 to consistently coincide with each other when a voltage is notapplied between the first electrode 32A and the second electrode 32B (orthe sub-electrodes 32A′ and 32B′), and the direction of the optical axisAX3 and the direction of the optical axis AX4 may be slightly deviatedfrom each other due to, for example, a manufacturing error.

Moreover, the optical axis AX4 is parallel to the light incident surface10A of the light guide plate 10 as well as parallel to a normal to thesurface of the transparent substrate 31 when a voltage is not appliedbetween the first electrode 32A and the second electrode 32B (or thesub-electrodes 32A′ and 32B′). In other words, when a voltage is notapplied between the first electrode 32A and the second electrode 32B (orthe sub-electrodes 32A′ and 32B′), the optical axis AX4 is orthogonal toa plane including the first electrode 32A and the second electrode 32B(or the sub-electrodes 32A′ and 32B′).

On the other hand, the bulk 64A is structured to have a fixed opticalaxis AX3 irrespective of whether or not a voltage is applied between thefirst electrode 32A and the second electrode 32B (or the sub-electrodes32A′ and 32B′). More specifically, the optical axis AX3 is parallel tothe light incident surface 10A of the light guide plate 10 as well asparallel to the normal to the surface of the transparent substrate 31.In other words, when a voltage is not applied between the firstelectrode 32A and the second electrode 32B (or the sub-electrodes 32A′and 32B′), the optical axis AX3 is parallel to the optical axis AX4.

It is to be noted that it is not necessary for the optical axis AX4 tobe consistently parallel to the light incident surface 10A of the lightguide plate 10 as well as the normal to the surface of the transparentsubstrate 31, and the optical axis AX4 may be aligned in a directionintersecting with one or both of the light incident surface 10A and thenormal to the surface of the transparent substrate 31 at a small angledue to, for example, a manufacturing error.

In this case, ordinary refractive indices of the bulk 64A and themicroparticle 64B are preferably equal to each other, and extraordinaryrefractive indices of the bulk 64A and the microparticle 64B arepreferably equal to each other. In this case, for example, when avoltage is not applied between the first electrode 32A and the secondelectrode 32B (or the sub-electrodes 32A′ and 32B′), there is littledifference in refractive index in all directions including the frontdirection and the oblique direction, and high transparency is obtained.Therefore, for example, light toward the front direction and lighttoward the oblique direction pass through the light modulation layer 64without being scattered in the light modulation layer 64. As a result,as illustrated in FIGS. 8(A) and (B), the light L from the light source20 (light from the oblique direction) is totally reflected by aninterface (an interface between the transparent substrate 31 or thelight guide plate 10 and the air) of a transparent region (thetransmission region 30A) in the light modulation device 60, andluminance (luminance in black display) of the transmission region 30A isdecreased, compared to the case where the light modulation device 60 isnot included (indicated by the alternate long and short dash line inFIG. 8(B)).

Moreover, for example, as illustrated in FIG. 14, the bulk 64A and themicroparticle 64B are structured to allow the directions of the opticalaxis AX3 and the optical axis AX4 to be different from (intersect withor be orthogonal to) each other when a voltage is applied between thefirst electrode 32A and the second electrode 32B (or the sub-electrodes32A′ and 32B′). Further, for example, the microparticles 64B arestructured to allow the optical axis AX4 to be parallel to the normal tothe light incident surface 10A of the light guide plate 10 as well asparallel to the surface of the transparent substrate 31 when a voltageis applied between the first electrode 32A and the second electrode 32B(or the sub-electrodes 32A′ and 32B′). In other words, when a voltage isapplied between the first electrode 32A and the second electrode 32B (orthe sub-electrodes 32A′ and 32B′), the optical axis AX4 is parallel to aplane including the first electrode 32A and the second electrode 32B (orthe sub-electrodes 32A′ and 32B′) as well as intersects with (or isorthogonal to) the extending direction of comb teeth of thesub-electrodes 32A′ and 32B′.

Therefore, when a voltage is applied between the first electrode 32A andthe second electrode 32B (or the sub-electrodes 32A′ and 32B′), in thelight modulation layer 64, a difference in refractive index in alldirections in a plane which is parallel to the normal to the lightincident surface 10A as well as is orthogonal to the surface of thetransparent substrate 31 is increased to obtain a high scatteringproperty. Accordingly, for example, light toward the front direction andlight toward the oblique direction are scattered in the light modulationlayer 64. As a result, for example, as illustrated in FIGS. 8(A) and(B), the light L from the light source 20 (light from the obliquedirection) passes through an interface (an interface between thetransparent substrate 31 or the light guide plate 10 and the air) of thescattering region 30B, and light having passed toward the reflectiveplate 40 is reflected by the reflective plate 40 to pass through thelight modulation device 60. Therefore, the luminance of the scatteringregion 30B is extremely higher than that in the case where the lightmodulation device 60 is not included (indicated by the alternate longand short dash line in FIG. 8(B)), and luminance in white display ispartially increased (partial luminance enhancement) by a reduced amountof the luminance of the transmission region 30A.

It is to be noted that the ordinary refractive indices of the bulk 64Aand the microparticle 64B may be slightly different from each other dueto, for example, a manufacturing error, and are preferably, for example,0.1 or less, and more preferably 0.05 or less. Moreover, theextraordinary refractive indices of the bulk 64A and the microparticle64B may be slightly different from each other due to, for example, amanufacturing error, and are preferably, for example, 0.1 or less, andmore preferably 0.05 or less.

Moreover, a refractive index difference (=extraordinary refractiveindex−ordinary refractive index) in the bulk 64A and a refractive indexdifference (=extraordinary refractive index−ordinary refractive index)in the microparticle 64B are preferably as large as possible, and arepreferably 0.05 or over, more preferably 0.1 or over, and still morepreferably 0.15 or over. In the case where the refractive indexdifferences in the bulk 64A and the microparticle 64B are large, thescattering power of the light modulation layer 64 is enhanced to allowlight guide conditions to be easily disrupted, thereby allowing lightfrom the light guide plate 10 to be easily extracted.

Further, the bulk 64A and the microparticle 64B have different responsespeeds with respect to an electric field. The bulk 64A has, for example,a streaky structure or a porous structure which does not respond to anelectric field, or a rod-like structure having a response speed slowerthan that of the microparticle 64B. The bulk 64A is formed of, forexample, a polymer material obtained by polymerizing a low-molecularmonomer. The bulk 64A is formed, for example, by polymerizing, by one orboth of heat and light, a material (for example, a monomer) withorientation and polymerization which is aligned along the alignmentdirection of the microparticles 64B or the alignment directions of thealignment films 63 and 65. On the other hand, the microparticles 64Bmainly include, for example, a liquid crystal material, and have aresponse speed sufficiently higher than that of the bulk 64A. Examplesof the liquid crystal material (liquid crystal molecules) included inthe microparticles 64B include rod-like molecules.

In this case, when a voltage is not applied between the first electrode32A and the second electrode 32B (the sub-electrodes 32A′ and 32B′), thelong-axis directions of the liquid crystal molecules in themicroparticles 64B are parallel to the optical axis AX3. At this time,the long axes of the liquid crystal molecules in the microparticles 64Bare parallel to the light incident surface 10A of the light guide plate10 as well as parallel to the direction of the normal to the surface ofthe transparent substrate 31. Moreover, when a voltage is appliedbetween the first electrode 32A and the second electrode 32B (or thesub-electrodes 32A′ and 32B′), the long-axis directions of the liquidcrystal molecules in the microparticles 64B intersect with (or areorthogonal to) the optical axis AX3. At this time, the long axes of theliquid crystal molecules in the microparticles 64B are parallel to thenormal to the light incident surface 10A of the light guide plate 10 aswell as parallel to the surface of the transparent substrate 31.

The above-described monomer having orientation and polymerization may bea material having optical anisotropy and forming a composite materialwith a liquid crystal; however, a low-molecular monomer which is curedwith ultraviolet light is preferable in this embodiment. It ispreferable that, in a state where no voltage is applied, directions ofoptical anisotropy of the liquid crystal and a resultant (a polymermaterial) formed by polymerizing a low-molecular monomer coincide witheach other; therefore, before curing the low-molecular monomer withultraviolet light, the liquid crystal and the low-molecular monomer arepreferably aligned in the same direction. In the case where a liquidcrystal is used as the microparticles 64B, when the liquid crystalincludes rod-like molecules, the used monomer material preferably has arod-like shape. As described above, a material having both ofpolymerization and liquid crystal properties is preferably used as themonomer material, and, for example, the monomer material preferablyincludes one or more functional groups selected from the groupconsisting of an acrylate group, a methacrylate group, an acryloyloxygroup, a methacryloyloxy group, a vinyl ether group, and an epoxy groupas polymerizable functional groups. These functional groups are allowedto be polymerized by ultraviolet, infrared, or electron irradiation, orby heating. To suppress a reduction in the degree of alignment underultraviolet irradiation, a liquid crystal material having apolyfuncitonal group may be added. In the case where the bulk 64A hasthe above-described streaky structure, as the material of the bulk 64A,a bifunctional liquid crystal monomer is preferably used. Moreover, amonofunctional monomer may be added to the material of the bulk 64A toadjust a temperature at which liquid crystal properties are exhibited,or a tri- or more-functional monomer may be added to the material of thebulk 64A to improve crosslink density.

Next, functions and effects of the backlight 2 according to theembodiment will be described below.

In the backlight 2 according to the embodiment, a voltage is appliedbetween the sub-electrodes 32A′ and 32B′ of respective light modulationcells 30S to allow the optical axes AX4 of the microparticles 64B in onelight modulation cell 30S to be parallel or substantially parallel tothe optical axis AX3 of the bulk 64A, and to allow the optical axes AX4of the microparticles 64B in another light modulation cell 30S tointersect with or be orthogonal to the optical axis AX3 of the bulk 64A.As a result, light emitted from the light source 20 and entering intothe light guide plate 10 passes through the transmission region 30Awhere the optical axes AX3 and AX4 are parallel or substantiallyparallel to each other of the light modulation device 60. On the otherhand, light emitted from the light source 20 and entering into the lightguide plate 10 is scattered in the scattering region 30B where theoptical axes AX3 and AX4 intersect with or are orthogonal to each otherof the light modulation device 60. Light having passed through a bottomsurface of the scattering region 30B in the scattered light is reflectedby the reflective plate 40 to be returned to the light guide plate 10again, and then the light is emitted from a top surface of the backlight2. Moreover, light toward a top surface of the scattering region 30B inthe scattered light passes through the light guide plate 10, and then isemitted from the top surface of the backlight 2. Thus, in theembodiment, light is hardly emitted from the top surface of thetransmission region 30A, and light is emitted from the top surface ofthe scattering region 30B. Accordingly, a modulation ratio in a frontdirection is increased.

On the other hand, in the embodiment, as the bulk 64A and themicroparticles 64B each include mainly an optical anisotropic material,the scattering property in an oblique direction is reduced, therebyenabling to improve transparency. For example, the bulk 64A and themicroparticles 64B include mainly the optical anisotropic materials withordinary refractive indices which are equal to each other andextraordinary refractive indices which are also equal to each other, andin addition thereto, the directions of the optical axes of the bulk 64Aand the microparticles 64B coincide with or substantially coincide witheach other in a region where a voltage is not applied between thesub-electrodes 32A′ and 32B′. Therefore, the refractive index differenceis reduced or eliminated in all directions including the front direction(a direction of the normal to the light modulation device 60) and theoblique direction, thereby obtaining high transparency. As a result, theleakage of light in a range having a large view angle is allowed to bereduced or substantially eliminated, and view angle characteristics areallowed to be improved.

For example, when a liquid crystal having an ordinary refractive indexof 1.5 and an extraordinary refractive index of 1.65, and a liquidcrystal monomer having an ordinary refractive index of 1.5 and anextraordinary refractive index of 1.65 are mixed, and the liquid crystalmonomer is polymerized in a state where the liquid crystal and theliquid crystal monomer are aligned by an alignment film or an electricfield, the optical axis of the liquid crystal and the optical axis of apolymer formed by polymerizing the liquid crystal monomer coincide witheach other. Therefore, the refractive indices coincide with each otherin all directions, thereby enabling to achieve a state wheretransparency is high, and to further improve the view anglecharacteristics.

Moreover, in the embodiment, for example, as illustrated in FIGS. 8(A)and (B), luminance in the transmission region 30A (luminance in blackdisplay) is lower, compared to the case where the light modulationdevice 60 is not included (indicated by the alternate long and shortdash line in FIG. 8(B)). On the other hand, luminance in the scatteringregion 30B is significantly increased, compared to the case where thelight modulation device 60 is not included (indicated by the alternatelong and short dash line in FIG. 8(B)), and luminance in white displayis partially increased (partial luminance enhancement) by a reducedamount of the luminance of the transmission region 30A. It is because asthe bulk 64A and the microparticles 64B each include mainly the opticalanisotropic material, the scattering property in the oblique directionis suppressed to reduce leak light from the light guide plate in a darkstate. Therefore, as light is guided from a part in a partially-darkstate to a part in a partially-bright state, partial luminanceenhancement is achievable without increasing electric power supplied tothe backlight 2.

Moreover, in the embodiment, the electrode 32 is disposed on only thesurface of the transparent substrate 31 in the pair of transparentsubstrates 31 and 36 which allow the light modulation layer 64 to besandwiched therebetween. Therefore, for example, in the case where theelectrode 32 is configured of an ITO film, a light absorption amount bythe electrode 32 when light emitted from the light source 20 repeatedlypasses through the electrode 32 in the light modulation device 60 whilepropagating through the light guide plate 10 is smaller, compared to thecase where the electrodes are disposed on the surfaces of both of thetransparent substrates 31 and 36 in the light modulation device 60.Further, as the light absorption amount by the electrode 32 is small, achange in chromaticity of illumination light in a plane is also small.As a result, chromaticity of illumination light is allowed to be furtheruniformized while suppressing a reduction in light extractionefficiency.

3. Modifications First Modification

In the above-described embodiments, the comb teeth of the firstelectrode 32A and the second electrode 32B extend in a directionparallel to the extending direction of the light source 20; however, forexample, as illustrated in FIGS. 15(A) and (B), they may extend in adirection intersecting with the extending direction of the light source20. At this time, the first electrode 32A and the second electrode 32Beach may be configured of, for example, a single structure formed on anentire surface of the transparent substrate 31 as illustrated in FIGS.15(A) to (C), or may be configured of, for example, a plurality ofstructures (sub-electrodes 32A′ and 32B′) as illustrated in FIGS. 16(A)to (C).

FIG. 17 schematically illustrates an example of an alignment state inthe bulk 34A and the microparticles 34B when a voltage is not applied tothe first electrode 32A and the second electrode 32B (or thesub-electrodes 32A′ and 32B′). FIG. 18 schematically illustrates anexample of an alignment state in the bulk 34A and the microparticles 34Bwhen a voltage is applied to the first electrode 32A and the secondelectrode 32B (or the sub-electrodes 32A′ and 32B′).

For example, as illustrated in FIG. 17, the bulk 34A and themicroparticle 34B are structured to allow the direction of the opticalaxis AX1 of the bulk 34A (the long axis of the ellipsoid 134A) and thedirection of the optical axis AX2 of the microparticle 34B (the longaxis of the ellipsoid 134B) to coincide with (be parallel to) each otherwhen a voltage is not applied between the first electrode 32A and thesecond electrode 32B (or the sub-electrodes 32A′ and 32B′).

Moreover, the optical axis AX2 is parallel to the normal to the lightincident surface 10A of the light guide plate 10 as well as parallel tothe surface of the transparent substrate 31 when a voltage is notapplied between the first electrode 32A and the second electrode 32B (orthe sub-electrodes 32A′ and 32B′). In other words, when a voltage is notapplied between the first electrode 32A and the second electrode 32B (orthe sub-electrodes 32A′ and 32B′), the optical axis AX2 is parallel to aplane including the first electrode 32A and the second electrode 32B (orthe sub-electrodes 32A′ and 32B′) as well as parallel to the extendingdirection of the comb teeth of the first electrode 32A and the secondelectrode 32B (or the sub-electrodes 32A′ and 32B′). It is to be notedthat it is not necessary for the directions of the optical axis AX1 andthe optical axis AX2 to consistently coincide with each other when avoltage is not applied between the first electrode 32A and the secondelectrode 32B (or the sub-electrodes 32A′ and 32B′), and the directionof the optical axis AX1 and the direction of the optical axis AX2 may beslightly deviated from each other due to, for example, a manufacturingerror.

On the other hand, for example, the bulk 34A is structured to have afixed optical axis AX1 irrespective of whether or not a voltage isapplied between the first electrode 32A and the second electrode 32B (orthe sub-electrodes 32A′ and 32B′). More specifically, the optical axisAX1 is parallel to the normal to the light incident surface 10A of thelight guide plate 10 as well as parallel to the surface of thetransparent substrate 31. In other words, when a voltage is not appliedbetween the first electrode 32A and the second electrode 32B (or thesub-electrodes 32A′ and 32B′), the optical axis AX1 is parallel to theoptical axis AX2. It is to be noted that it is not necessary for theoptical axis AX2 to be consistently parallel to the normal to the lightincident surface 10A of the light guide plate 10 as well as the surfaceof the transparent substrate 31, and the optical axis AX2 may be alignedin a direction intersecting with one or both of the normal to the lightincident surface 10A and the surface of the transparent substrate 31 ata small angle due to, for example, a manufacturing error.

Moreover, for example, as illustrated in FIG. 18, the bulk 34A and themicroparticles 34B are structured to allow directions of the opticalaxes AX1 and AX2 to be different from (intersect with or be orthogonalto) each other when a voltage is applied between the first electrode 32Aand the second electrode 32B (or the sub-electrodes 32A′ and 32B′).Further, for example, the microparticles 34B are structured to allow theoptical axis AX2 to be parallel to the light incident surface 10A of thelight guide plate 10 as well as parallel to the surface of thetransparent substrate 31 when a voltage is applied between the firstelectrode 32A and the second electrode 32B (or the sub-electrodes 32A′and 32B′). In other words, when a voltage is applied between the firstelectrode 32A and the second electrode 32B (or the sub-electrodes 32A′and 32B′), the optical axis AX2 is parallel to a plane including thefirst electrode 32A and the second electrode 32B (or the sub-electrodes32A′ and 32B′) and intersects with (or is orthogonal to) the extendingdirection of comb teeth of the sub-electrodes 32A′ and 32B′.

FIG. 19 schematically illustrates an example of an alignment state inthe bulk 64A and the microparticles 64B in the above-describedmodification when a voltage is not applied to the first electrode 32Aand the second electrode 32B (or the sub-electrodes 32A′ and 32B′). FIG.20 schematically illustrates an example of an alignment state in thebulk 64A and the microparticles 64B in the above-described modificationwhen a voltage is applied between the first electrode 32A and the secondelectrode 32B (or the sub-electrodes 32A′ and 32B′).

For example, as illustrated in FIG. 19, the bulk 64A and themicroparticle 64B are structured to allow the direction of the opticalaxis AX3 of the bulk 64A (the long axis of the ellipsoid 164A) and thedirection of the optical axis AX4 of the microparticle 64B (the longaxis of the ellipsoid 164B) to coincide with (be parallel to) each otherwhen a voltage is not applied between the first electrode 32A and thesecond electrode 32B (or the sub-electrodes 32A′ and 32B′). Moreover, itis not necessary for the directions of the optical axis AX3 and theoptical axis AX4 to consistently coincide with each other when a voltageis not applied between the first electrode 32A and the second electrode32B (or the sub-electrodes 32A′ and 32B′), and the direction of theoptical axis AX3 and the direction of the optical axis AX4 may beslightly deviated from each other due to, for example, a manufacturingerror.

Moreover, the optical axis AX4 is parallel to the light incident surface10A of the light guide plate 10 as well as parallel to the normal to thesurface of the transparent substrate 31 when a voltage is not appliedbetween the first electrode 32A and the second electrode 32B (or thesub-electrodes 32A′ and 32B′). In other words, when a voltage is notapplied between the first electrode 32A and the second electrode 32B (orthe sub-electrodes 32A′ and 32B′), the optical axis AX4 is orthogonal toa plane including the first electrode 32A and the second electrode 32B(or the sub-electrodes 32A′ and 32B′).

On the other hand, the bulk 64A is structured to have a fixed opticalaxis AX3 irrespective of whether or not a voltage is applied between thefirst electrode 32A and the second electrode 32B (or the sub-electrodes32A′ and 32B′). More specifically, the optical axis AX3 is parallel tothe light incident surface 10A of the light guide plate 10 as well asparallel to the normal to the surface of the transparent substrate 31.In other words, when a voltage is not applied between the firstelectrode 32A and the second electrode 32B (or the sub-electrodes 32A′and 32B′), the optical axis AX3 is parallel to the optical axis AX4.

It is to be noted that it is not necessary for the optical axis AX4 tobe consistently parallel to the light incident surface 10A of the lightguide plate 10 as well as the normal to the surface of the transparentsubstrate 31, and the optical axis AX4 may be aligned in a directionintersecting with one or both of the light incident surface 10A and thenormal to the surface of the transparent substrate 31 at a small angledue to, for example, a manufacturing error.

Moreover, for example, as illustrated in FIG. 20, the bulk 64A and themicroparticles 64B are structured to allow directions of the opticalaxis AX3 and the optical axis AX4 to be different from (intersect withor be orthogonal to) each other when a voltage is applied between thefirst electrode 32A and the second electrode 32B (or the sub-electrodes32A′ and 32B′). Further, for example, the microparticles 64B arestructured to allow the optical axis AX4 to be parallel to the lightincident surface 10A of the light guide plate 10 as well as parallel tothe surface of the transparent substrate 31 when a voltage is appliedbetween the first electrode 32A and the second electrode 32B (or thesub-electrodes 32A′ and 32B′). In other words, when a voltage is appliedbetween the first electrode 32A and the second electrode 32B (or thesub-electrodes 32A′ and 32B′), the optical axis AX4 is parallel to aplane including the first electrode 32A and the second electrode 32B (orthe sub-electrodes 32A′ and 32B′) as well as intersects with (or isorthogonal to) the extending direction of comb teeth of thesub-electrodes 32A′ and 32B′.

In the above-described modification, when the alignment states in thebulk 34A and the microparticles 34B or the alignment states in the bulk64A and the microparticles 64B are as illustrated in the above FIGS. 17to 19, the luminance in the scattering region 30B is significantlyincreased, compared to the case where the light modulation devices 30and 60 are not included (indicated by the alternate long and short dashline in FIG. 8(B)), and luminance in white display is partiallyincreased (partial luminance enhancement) by a reduced amount of theluminance of the transmission region 30A.

Moreover, in the above-described modification, as in the case of theabove-described embodiments and the like, the electrode 32 is disposedon only the surface of the transparent substrate 31 in the pair oftransparent substrates 31 and 36. Therefore, for example, in the casewhere the electrode 32 is configured of an ITO film, a light absorptionamount by the electrode 32 when light emitted from the light source 20repeatedly passes through the electrode 32 in the light modulationdevice 30 or 60 while propagating through the light guide plate 10 issmaller, compared to the case where the electrodes are disposed on thesurfaces of both of the transparent substrates 31 and 36 in the lightmodulation device 30 or 60. Further, as the light absorption amount bythe electrode 32 is small, a change in chromaticity of illuminationlight in a plane is also small. As a result, chromaticity ofillumination light is allowed to be further uniformized whilesuppressing a reduction in light extraction efficiency.

Second Modification

In the above-described embodiments and modifications thereof, as thelight guide plate 10, a light guide plate with a pattern shape allowinglight incident from the light incident surface 10A to be scattered to beuniformized, or a flat light guide plate without such a pattern shape isused; however, for example, as illustrated in FIG. 21(A), a light guideplate having a plurality of strip-like projections 11 on a top surfacethereof may be used. It is to be noted that, for example, as illustratedin FIG. 21(B), the light guide plate 10 may have a plurality ofstrip-like projections 11 on a bottom surface thereof. Moreover, forexample, the light guide plate 10 may have a plurality of strip-likeprojections 11 in the light guide plate 10 (not illustrated). Further,the light guide plate 10 may be hollow, or may be densely packed.

The respective projections 11 extend in a direction parallel to thenormal to the light incident surface 10A, and, for example, asillustrated in FIGS. 21(A) and (B), the projections 11 are successivelyformed from one side surface of the light guide plate 10 to another sidesurface facing the side surface. A section in an arrangement directionof each of the projections 11 has, for example, a rectangular shape, atrapezoidal shape, or a triangular shape. In the case where the sectionin the arrangement direction of each projection 11 has a rectangularshape, a rectilinear propagation property of light is extremely high,and the projections 11 are suitable for a large-scale backlight. In thecase where the section in the arrangement direction of each projection11 has a trapezoidal shape, processing of a die used to form eachprojection 11 by injection molding, extrusion molding, heat-pressmolding, or the like is easy, and mold releasability in molding is high,and yields and molding speed are allowed to be improved because of areduction in defects.

A flat surface may or may not be disposed between adjacent projections11. The height of each of the projections 11 may be uniform ornonuniform in a plane. For example, as illustrated in FIG. 22(A), whenone side surface of the light guide plate 10 is the light incidentsurface 10A, the height of each of the projections 11 may be smaller ona side closer to the light incident surface 10A, and be higher on a sidecloser to a side surface facing the light incident surface 10A.Moreover, for example, although not illustrated, when a pair of facingside surfaces of the side surfaces of the light guide plate 10 are lightincident surfaces 10A, the height of each of the projections 11 may belower at and in proximity to both of the light incident surfaces 10A,and be higher in other regions. The height at and in proximity to thelight incident surface 10A of each of the projections 11 may be zero orsubstantially zero. For example, as illustrated in FIG. 22(B), theheight of each of the projections 11 may be increased from a side closerto the light incident surface 10A to a side surface facing the lightincident surface 10A. At this time, the height of each of theprojections 11 may be uniform in a midway from the light incidentsurface 10A to the side surface facing the light incident surface 10A.It is to be noted that a plurality of projections 11 with a nonuniformheight as illustrated in FIGS. 22(A) and (B) may be disposed in a regionother than the top surface of the light guide plate 10, and, forexample, the plurality of projections 11 with a nonuniform height may bedisposed on the bottom surface of the light guide plate 10 or in thelight guide plate 10.

As described above, when the height of each of the projections 11 (inother words, the depth of a groove formed between the projections 11)varies, the rectilinear propagation property of light is allowed tovary. For example, as illustrated in FIGS. 21(A) and (B), in the casewhere the projections 11 are disposed on and in proximity to the lightincident surface 10A, and the light source 20 is configured of aplurality of light source blocks 25 capable of being drivenindependently of one another, for example, as illustrated in FIG. 23(A),when one light source block 25 illuminates, light L1 emitted from thelight source block 25 propagates through the light guide plate 10 whilenot spreading too much in a horizontal direction (a width direction). Inthis case, a dark region may be generated between the point-like lightsources 21 in proximity to the light incident surface 10A, and in thiscase, image quality may be degraded. Therefore, in such a case, forexample, as illustrated in FIGS. 22(A) and (B), the height of each ofthe projections 11 is preferably lower or zero at and in proximity tothe light incident surface 10A. In doing so, for example, as illustratedin FIG. 23(B), the light L1 emitted from the light source block 25 isallowed to be spread in the horizontal direction (the width direction)at a divergent angle of the point-like light source 23 at and inproximity to the light incident surface 10A, thereby enabling topropagate with a substantially uniform width in a region farther fromthe light incident surface 10A.

In this case, in the case were the electrode 32 is configured of aplurality of sub-electrode pairs 32C, when light emitted from the lightsource block 25 propagates through the light guide plate 10 as describedabove, partial lighting is allowed to be performed by applying a voltageto one sub-electrode pair 32C.

For example, in the case where the plurality of sub-electrode pairs 32C(light modulation cells 30S) extend in a direction parallel to the lightincident surface 10A and are arranged in a direction parallel to thenormal to the light incident surface 10A, and a voltage is applied toonly one light modulation cell 30S, as illustrated in FIG. 24(A), thelight L1 emitted from one light source block 25 is mostly emitted from asection where light emitted from one light source block 25 passes of thelight modulation cell 30S to which the voltage is applied. In this case,in a section profile of luminance in a direction parallel to the lightincident surface 10A in FIG. 24(A), a boundary between a lightingsection and a non-lighting section is moderately blurred; therefore, itis difficult to visually identify the boundary. As a result, contrast isallowed to be improved without reducing image quality.

Moreover, for example, in the case were the plurality of sub-electrodepairs 32C (the light modulation cells 30S) extend in a directionparallel to the normal to the light incident surface 10A and arearranged in a direction parallel to the light incident surface 10A, anda voltage is applied to only one light modulation cell 30S, asillustrated in FIG. 24(B), the light L1 emitted from one light sourceblock 25 is mostly emitted from a section where light emitted from onelight source block 25 passes (for example, the entire light modulationcell 30S to which the voltage is applied) of the light modulation cell30S to which the voltage is applied.

Further, for example, in the case where the plurality of sub-electrodepairs 32C (the light modulation cells 30S) are two-dimensionallyarranged and a voltage is applied to only one light modulation cell 30S,as illustrated in FIG. 24(C), the light L1 emitted from one light sourceblock 25 is mostly emitted from a section where light emitted from onelight source block 25 passes (for example, the entire light modulationcell 30S to which the voltage is applied) of the light modulation cell30S to which the voltage is applied.

In the above-described respective examples, in the case where the heightof each of the projections 11 of the light guide plate 10 is smaller atand in proximity to the light incident surface 10A, even if a voltage isapplied to the light modulation cells 30S in proximity to the lightincident surface 10A to allow the light L1 to be emitted from a sectionin proximity to the light incident surface 10A, in-plane luminance ofthe light L1 (illumination light) emitted from the light modulationcells 30A is allowed to be further uniformized

Third Modification

In the above-described embodiments and modifications thereof, the lightmodulation devices 30 and 60 each are in close contact with and arebonded to the back side (the bottom surface) of the light guide plate 10without an air layer in between; however, for example, as illustrated inFIG. 25, the light modulation devices 30 and 60 each may be in closecontact with and bonded to the top surface of the light guide plate 10without an air layer in between. Moreover, for example, as illustratedin FIG. 26, the light modulation devices 30 and 60 each may be disposedin the light guide plate 10. However, also in this case, it is necessaryfor the light modulation devices 30 and 60 to be in close contact withand bonded to the light guide plate 10 without an air layer in between.

Moreover, in the above-described embodiments, no component isspecifically disposed on the light guide plate 10; however, for example,as illustrated in FIG. 27, an optical sheet 70 (for example, a diffuserplate, a diffuser sheet, a lens film, a polarization splitter sheet, orthe like) may be disposed. In such a case, a part of light emitted fromthe light guide plate 10 in an oblique direction rises in the frontdirection; therefore, a modulation ratio is allowed to be effectivelyimproved.

Fourth Modification

Moreover, in the above-described respective embodiments andmodifications thereof, one or both of the transparent substrate 31 andthe transparent substrate 37 may be integrally formed with the lightguide plate 10. For example, in the above-described embodiments andmodifications thereof, in the case where the transparent substrate 37 isin contact with the light guide plate 10, the transparent substrate 37may be integrally formed with the light guide plate 10. At this time,the transparent substrate 37 corresponds to a specific example of “firsttransparent substrate” or “second transparent substrate”. Moreover, forexample, in the above-described respective embodiments and modificationsthereof, in the case where the transparent substrate 31 is in contactwith the light guide plate 10, the transparent substrate 31 may beintegrally formed with the light guide plate 10. At this time, thetransparent substrate 31 corresponds to a specific example of “firsttransparent substrate” or “second transparent substrate”. Further, forexample, in the above-described respective embodiments and modificationsthereof, in the case where the transparent substrates 31 and 37 are incontact with the light guide plate 10, the transparent substrates 31 and37 may be integrally formed with the light guide plate 10. At this time,the transparent substrate 31 or the transparent substrate 37 correspondsto a specific example of “first transparent substrate” or “secondtransparent substrate”.

Application Example

Next, an application example of the backlights 1 and 2 according to theabove-described embodiments will be described below.

FIG. 28 illustrates an example of a schematic configuration of a display3 according to the application example. The display 3 includes a displaypanel 80, and the backlight 1 or 2 disposed behind the display panel 80.

The display panel 80 displays an image. The display panel 80 includes aplurality of pixels which are arranged in a matrix, and is allowed todisplay an image by driving the plurality of pixels based on an imagesignal. The display panel 80 is, for example, a transmissive liquidcrystal display panel, and has a configuration in which a liquid crystallayer is sandwiched between a pair of transparent substrates. Althoughnot illustrated, the display panel 80 includes, for example, apolarizer, a transparent substrate, pixel electrodes, an alignment film,a liquid crystal layer, an alignment film, a common electrode, a colorfilter, a transparent substrate, and a polarizer in order from a sidecloser to the backlight 1 or 2.

The transparent substrates are configured of substrates transparent tovisible light, for example, plate glass. It is to be noted that anactive drive circuit (not illustrated) including TFTs (thin filmtransistors), wiring, and the like electrically connected to the pixelelectrodes is formed on the transparent substrate located closer to thebacklight 1. The pixel electrodes and the common electrode are made of,for example, indium tin oxide (ITO). The pixel electrodes are arrangedin a lattice arrangement or a delta arrangement on the transparentsubstrate, and function as electrodes for respective pixels. On theother hand, the common electrode is formed on an entire surface of thecolor filter, and functions as a common electrode facing the respectivepixel electrodes. The alignment films are made of a polymer materialsuch as polyimide, and perform an alignment process on a liquid crystal.The liquid crystal layer is made of, for example, a VA (VerticalAlignment) mode, TN (Twisted Nematic) mode or STN (Super TwistedNematic) mode liquid crystal, and has a function of changing thedirection of a polarizing axis of emitted light from the backlight 1 or2 in each pixel by a voltage applied from the drive circuit (notillustrated). It is to be noted that liquid crystal alignment is changedin a stepwise manner to adjust the direction of a transmission axis ofeach pixel in a stepwise manner. In the color filter, color filtersseparating light having passed through the liquid crystal layer into,for example, three primary colors of red (R), green (G), and blue (B),or four colors such as R, G, B, and white (W), respectively, arearranged corresponding to the arrangement of the pixel electrodes.Typical filter arrangements (pixel arrangements) include a stripearrangement, a diagonal arrangement, a delta arrangement, and arectangular arrangement.

The polarizers are optical shutters of one kind, and allow only light(polarized light) in a certain vibration direction to pass therethrough.It is to be noted that the polarizers may be absorption polarizersabsorbing light (polarized light) in a vibration direction other than atransmission axis, but the polarizers are preferably reflectivepolarizers reflecting light toward the backlight 1 or 2 in terms of animprovement in luminance. The polarizers are disposed to allow theirpolarizing axes to be different by 90° from each other, thereby allowingemitted light from the backlight 1 to pass therethrough via the liquidcrystal layer, or to be shielded.

For example, the drive circuit 50 controls the magnitude of a voltageapplied to the sub-electrodes 32A′ and 32B′ of each of the lightmodulation cells 30S to allow the optical axes AX2 or AX4 of themicroparticles 34B or 64B in a cell corresponding to a black-displaypixel position of the plurality of light modulation cells 30S to beparallel to the optical axis AX1 or AX3 of the bulk 34A or 64A, as wellas to allow the optical axes AX2 or AX4 of the microparticles 34B or 64Bin a cell corresponding to a white-display pixel position of theplurality of light modulation cells 30S to intersect with the opticalaxis AX1 or AX3 of the bulk 34A or 64A.

In the application example, as a light source applying light to thedisplay panel 80, the backlight 1 or 2 according to the above-describedembodiments is used. Therefore, while the leakage of light in a rangehaving a large view angle is allowed to be reduced or substantiallyeliminated, display luminance is allowed to be improved. As a result, amodulation ratio in a front direction is allowed to be increased.Moreover, partial luminance enhancement is achievable without increasingelectric power supplied to the backlight 1 or 2.

Moreover, in the application example, the backlight 1 or 2 partiallymodulates intensity of light entering into the display panel 80 based ona display image. However, when an abrupt change in brightness occurs inpattern edge sections of the sub-electrodes 32A′ and 32B′ included inthe light modulation device 30 or 60, a boundary section thereof isobserved even in a display image. Therefore, a characteristic, calledblur characteristic, is demanded to change brightness at an electrodeboundary section as monotonously as possible. A diffuser plate with highdiffusibility is effectively used to enhance the blur characteristic;however, when diffusibility is high, total light beam transmittance isreduced, thereby causing a tendency to reduce brightness. Therefore, inthe application example, when a diffuser plate is used as the opticalsheet 70, the total light beam transmittance of the diffuser plate ispreferably 50% to 85%, and more preferably 60% to 80%. Moreover, theblur characteristic is improved with an increase in spatial distancebetween the light guide plate 10 and the diffuser plate in the backlight1 or 2.

Further, in the case where a light guide plate including a plurality ofprojections 11 on a top surface thereof is used as the light guide plate10, and an electrode configured of a plurality of sub-electrode pairs32C is used as the electrode 32, and a plurality of light source blocks25 capable of being driven independently of one another are used as thelight source 20, when only some of the light source blocks 25 illuminateand a voltage is applied to some of the sub-electrode pairs 32C, theblur characteristic is improved. Moreover, when the number ofsub-electrode pairs 32C included in the light modulation device 30 isincreased and a voltage applied to respective sub-electrode pairs 32C isadjusted to change lightness or darkness as monotonously as possible,the blur characteristic is improved.

It should be understood that various changes and modifications to thepresently preferred embodiments described herein will be apparent tothose skilled in the art. Such changes and modifications can be madewithout departing from the spirit and scope of the present subjectmatter and without diminishing its intended advantages. It is thereforeintended that such changes and modifications be covered by the appendedclaims.

The invention claimed is:
 1. An illumination unit comprising: a firsttransparent substrate and a second transparent substrate disposed to beseparated from and face each other; a light source emitting light to anend surface of the first transparent substrate or the second transparentsubstrate; an electrode disposed on a surface of the first transparentsubstrate or the second transparent substrate and generating an electricfield in a direction parallel to the surface of the first transparentsubstrate; a light modulation layer disposed in a gap between the firsttransparent substrate and the second transparent substrate andexhibiting a scattering property or transparency with respect to lightfrom the light source, depending on magnitude of the electric field; anda drive circuit applying a voltage to the electrode, wherein theelectrode includes a plurality of separately driven sub-electrodegroups, each sub-electrode group including a first electrode having combteeth which extend in a first direction and a second electrode havingcomb teeth which are disposed alternately with the comb teeth of thefirst electrode, wherein a plurality of the sub-electrode groups arearranged in a direction normal to a side surface facing the light sourceof side surfaces of the first transparent substrate such that the drivecircuit may independently apply voltages to the respective sub-electrodegroups according to a distance from the light source.
 2. Theillumination unit according to claim 1, wherein the comb teeth of thefirst and second electrodes extend in a direction parallel to a sidesurface facing the light source of side surfaces of the firsttransparent substrate.
 3. The illumination unit according to claim 1,wherein the comb teeth of the first and second electrodes extend in adirection parallel to a normal to a side surface facing the light sourceof side surfaces of the first transparent substrate.
 4. The illuminationunit according to claim 1, wherein the plurality of sub-electrode groupsare two-dimensionally arranged.
 5. The illumination unit according toclaim 1, wherein the drive circuit applies a voltage to respectivesub-electrode groups, the voltage being modulated according to thedistance from the light source and an image signal.
 6. The illuminationunit according to claim 1, wherein the light source is configured of aplurality of light source blocks capable of being driven independentlyof one another.
 7. The illumination unit according to claim 6, whereinthe drive circuit applies, to respective light source blocks, a voltageor a current being modulated according to a distance from the lightsource to a sub-electrode group to which a voltage is to be applied andan image signal.
 8. The illumination unit according to claim 4, whereinthe first transparent substrate or the second transparent substrate hasa plurality of projections extending in a direction parallel to a normalto a side surface facing the light source of side surfaces of the firsttransparent substrate or the second transparent substrate.
 9. Theillumination unit according to claim 5, wherein a section in a directionorthogonal to a projection extending direction of each of theprojections has a rectangular shape, a trapezoidal shape, or atriangular shape.
 10. The illumination unit according to claim 5,wherein a height of each of the projections is smaller at a shorterdistance from the light source and larger at a longer distance from thelight source.
 11. The illumination unit according to claim 8, whereinthe height of each of the projections is zero closest to the lightsource.
 12. The illumination unit according to claim 1, wherein thelight modulation layer exhibits transparency when a voltage is notapplied to the electrode and exhibits a scattering property when avoltage is applied to the electrode.
 13. The illumination unit accordingto claim 1, wherein the light modulation layer is configured byincluding liquid crystal molecules and a polymer, the liquid crystalmolecules having faster response speed with respect to an electric fieldgenerated by the electrode, the polymer having slower response speedwith respect to the electric field generated by the electrode.
 14. Theillumination unit according to claim 10, wherein the liquid crystalmolecules and the polymer are aligned in an extending direction of thecomb teeth of the first electrode when a voltage is not applied to theelectrode.
 15. The illumination unit according to claim 10, wherein theliquid crystal molecules and the polymer are aligned in a direction of anormal to the first transparent substrate when a voltage is not appliedto the electrode.
 16. A display comprising: a display panel including aplurality of pixels arranged in a matrix and being driven based on animage signal; and an illumination unit illuminating the display panel,the illumination unit including a first transparent substrate and asecond transparent substrate disposed to be separated from and face eachother, a light source emitting light to an end surface of the firsttransparent substrate or the second transparent substrate, an electrodedisposed on a surface of the first transparent substrate or the secondtransparent substrate and generating an electric field in a directionparallel to the surface of the first transparent substrate, a lightmodulation layer disposed in a gap between the first transparentsubstrate and the second transparent substrate and exhibiting ascattering property or transparency with respect to light from the lightsource, depending on magnitude of the electric field, and a drivecircuit applying a voltage to the electrode, wherein the electrodeincludes a plurality of separately driven sub-electrode groups, eachsub-electrode group including a first electrode having comb teeth whichextend in a first direction and a second electrode having comb teethwhich are disposed alternately with the comb teeth of the firstelectrode, wherein a plurality of the sub-electrode groups are arrangedin a direction normal to a side surface facing the light source of sidesurfaces of the first transparent substrate such that the drive circuitmay independently apply voltages to the respective sub-electrode groupsaccording to a distance from the light source.